Walking through the vineyard, we sometimes notice rose bushes in front of the rows of vines. It is often very pleasing to the eye, but has a precise function: to warn the winemaker of the appearance of powdery mildew , a disease caused by a fungus as destructive as downy mildew . The rose garden being more sensitive than the vine to powdery mildew, will be its first victim, thus warning the vine grower of an imminent attack on his vines.
In the past, another, more folkloric explanation was given: the rose bush planted at the end of the row served as a signal to the horse which, seeing it and by reflection, turned around to enter the next row.
Why can late blight be fatal to the crop?
Less "famous" than phylloxera, downy mildew is nevertheless the winemaker's worst enemy. It is a fungus, Plasmopara viticola, native to the eastern United States, introduced to Europe in the 1870s, probably via phylloxera-resistant rootstocks that have been found imported from the United States.
This little mushroom, which has conquered the whole world, particularly loves warm and humid climates: its spores germinate in spring and then thrive according to the rhythm of the showers and the ambient humidity. It first attacks the leaves, which become covered with small round spots, then the twigs, which twist, and the berries turn brown.
Generally, mold causes an imbalance in the plant and makes photosynthesis difficult. Severe bouts of blight can lead to severe crop losses or an unhealthy harvest. Like phylloxera, downy mildew is an endemic disease, meaning the fungus overwinters in fallen leaves, infecting soils and waiting for the right time to grow again.